1. Field of the Invention
The present invention relates to a relay system, and more particularly, to a communication method of a mobile station through a relay and a communication method of a relay system, in which the mobile station requests relay through a relay station in accordance with channel status to minimize service delay and use resources efficiently.
2. Discussion of the Related Art
A relay station (hereinafter, referred to as ‘relay’) is used to increase cell coverage and throughput of a mobile communication system. The relay is supported by a mobile station of IEEE 802.16e/16m, and may have a part of functions of a base station. The relay is an active repeater which includes network entry and mobility functions of PMP based relay, RRM function, and security function. The relay decodes a signal received from a transmitting side and again encodes the decoded signal to transfer the encoded signal to a receiving side, thereby removing noise. Also, the relay serves as a digital amplifier that can obtain higher throughput by using higher data rate coding. On the other hand, the relay has a drawback in that delay may occur during decoding and encoding. Also, the relay should consider backward compatibility of a PMP mode.
Types of the relay are divided as follows in accordance with mobility.
First of all, a fixed RS is permanently fixed to be used to increase cell coverage or shade zones. Also, the fixed RS may serve as a simple repeater. A nomadic RS is temporarily provided when users increase unexpectedly, or can optionally move within a building. A mobile RS can be mounted on a public traffic means such as bus or subway.
A frame structure for supporting a relay in a broadband radio access system according to the related art is as illustrated in FIG. 1.
A downlink zone of a relay (Relay DL Zone) and its uplink zone (Relay UL Zone) are established within a frame structure of a base station (BS frame structure) and a frame structure of the relay (RS frame structure). Data transmitted from the base station to the relay are allocated to a downlink of the BS frame structure in a burst type, and data transmitted from the relay to a mobile station or another neighboring relay are allocated to a downlink zone of the RS frame structure.
When the mobile station or the neighboring relay transmits data to the base station, the data is transmitted via a Relay UL Zone allocated to each mobile station, and the relay transmits the data to the base station via an uplink region allocated to the relay.
In order that the base station requests mobile station downlink signal quality information in the mobile communication system according to the related art, CQICH channel and report request (REP-REQ)/report response (REP-RSP) MAC messages are operated as follows.
In order that the base station acquires signal quality information of a downlink for the mobile station, there is provided a method for previously allocating some zones from a two-dimensional map of an uplink to a CQICH dedicated channel and then designating a subchannel to be used by each mobile station. UL-MAP IE within UL-MAP previously allocates a zone for CQICH channel using a fast-feedback channel and then designates a slot for each mobile station using CQICH_Alloc_IE. For example, MS#1 can designate CQICH#1, MS#2 can designate CQICH#2 and CQICH#3, and MS#3 can designate CQICH#4. Once the CQICH zone is allocated, the mobile station transmits signal quality information to the allocated CQICH zone at a period set in the CQICH_Alloc_IE. If the mobile station cancels the allocated CQICH, i.e., if duration=0 is set in the CQICH_Alloc_IE, the mobile station does not transmit signal quality information to the base station.
Report request (REP-REQ), i.e., channel measurement report request message is used when the base station operated at a bandwidth less than 11 GHz requests downlink channel measurement results such as RSSI and CINR of the mobile station.
Report response (REP-RSP), i.e., channel measurement report response message is used to respond to channel measurements listed in the report request message received in the mobile station. The mobile station transmits the channel measurement report response message which includes the measurement results of channels listed in the channel measurement report request message. Types of reported channel quality are determined in accordance with types of channels currently used in communication between the base station and the mobile station.
In the mobile communication system according to the related art, the base station determines whether to communicate with a corresponding mobile station through a relay by directly receiving signal quality information of downlink/uplink channels from the mobile station or receiving uplink signal quality information of the mobile station, wherein the uplink signal quality information is received by the relay.
However, when channel status between the relay and the mobile station is deteriorated, channel status between the base station and the mobile station is deteriorated, or channel status of a neighboring relay within a cell is more excellent than that between the base station and the mobile station, a report procedure of the mobile station to the base station through the relay is not defined.
Also, a procedure for a mobile station which intends to continue to connect a service with another relay within the base station to switch relay stations is not defined clearly, wherein the service is relayed from the base station to the mobile station through the relay.